<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .fater{
            width: 400px;
            height: 400px;
            background-color: #756;
            position: relative;
        }

        .son{
            width: 100px;
            height: 100px;
            background-color: rgb(153, 95, 95);
            position: absolute;
            left: 50%;
            margin-left: -50px;
            top: 50%;
            margin-top: -50px;
        }
    </style>
</head>
<body>
    <div class="fater">
        <div class="son"></div>
    </div>
</body>
</html>